A natural laboratory to study plasma physics is represented by the solar wind. The solar wind is a multi-component and weakly collisional system, and is generally observed from spacecraft measurements to be in a fully turbulent regime. Therefore, the nonlinear dynamics of a collisionless plasma is well described by the self-consistent Vlasov theory, taking into account proton, alpha particle and electron dynamics.
We present Vlasov numerical simulations of a turbulent multi-ion plasma, using a low-noise hybrid Vlasov-Maxwell code in a five-dimensional phase space configuration (two dimensions in physical space and three dimensions in velocity space). Ions are treated as kinetic particles, so the Vlasov equation is solved for proton and alpha particle distribution functions, while electrons are considered as a fluid.
The ion dynamics at short spatial scales display several interesting aspects, mainly consisting in the departure of the distribution functions from the typical Maxwellian configuration, under the effect of the turbulence. During the nonlinear evolution, coherent structures appear, such as vortices and current sheets and, in between magnetic islands, reconnection events occur. In regions of high magnetic stress, temperature anisotropy is found to be higher.
Preferential perpendicular heating is observed for both ion species, although alpha particles display a more significant anisotropy. Moreover, according with the solar wind observations, the results show that the temperature anisotropy of alpha particles is correlated to the proton temperature anisotropy and to the alpha particle drift speed with respect to protons.
This study helps understanding some of the complex features commonly observed in the turbulent solar wind.